Dielectric paste and thick film capacitor using the same

ABSTRACT

Provided is a dielectric paste containing glass powder, lead perovskite compound dielectric powder and organic vehicle, wherein the glass powder has a composition represented by xBi2O3-yPbO-zSiO2 where x+y+z is 100 mol parts and the values of x, y and z are on lines or within a region enclosed by lines passing through five points A(25, 5, 70), B(10, 20, 70), C(10, 60, 30), D(35, 60, 5) and E(90, 5, 5) on a ternary diagram. The dielectric paste allows a minute dielectric film to be formed by sintering at a low temperature below 870 DEG  C.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to dielectric paste and a thick filmcapacitor using the same and more particularly to dielectric pasteuseful as a material for forming a load capacitor of a ceramicoscillator and a thick film capacitor using the same.

2. Related Art

A thick film capacitor is being used, for example, as a component of athick film integrated circuit. As a dielectric substance for such thickfilm capacitor, one which is mainly composed of barium titanate ceramicsand to which a glass component is added as desired is mainly used.

For instance, an example in which BaTiO₃ --CaSnO₃ --CaSiO₃ ceramics isused as the dielectric substance is described in Japanese PatentLaid-Open No. 51-48159 and an example in which BaTiO₃ --(Pb, Sr) (Ti,Sn)O₃ and glass are used as the dielectric substance is described inJapanese Patent Laid-Open No. 51-150097. The thick film capacitor isthen obtained by forming a dielectric paste by dispersing powder of theabove-mentioned dielectric substance and of glass, as desired, into anorganic vehicle, applying it on an insulated substrate such as aluminaby means of screen-printing or the like and then by sintering in air.

With the development of digital IC technology, a ceramic oscillatorusing piezoelectric ceramics has come to be used widely as a referencesignal (or clock signal) generating element in electronic equipment.Such a ceramic oscillator is normally connected to a load capacitorwhich conforms to temperature characteristics of a resonator which isnecessary in constructing an oscillating circuit. With theminiaturization of recent electronic equipment, the demand forminiaturization of the electronic parts such as the ceramic oscillatoris also increasing.

To that end, a trial using a thick film capacitor, instead of a discretetype capacitor, as a load capacitor to be connected to the ceramicoscillator has made to obtain a built-in capacitor ceramic oscillator.However, the thick film capacitor fabricated by using theabove-mentioned conventional dielectric paste has had problems asfollows.

That is, there has been a problem that the size of a dielectric filmobtained is inferior because the conventional dielectric paste containsa high amount of dielectric powder in order to obtain a high dielectricconstant. It is necessary to sinter at a high temperature exceeding 900°C. in order to complement the lack of the small size. However, sinteringat such high temperature may exert an adverse effect on other circuitelements already formed on the substrate before the sintering, such as acapacitor electrode for the thick film capacitor already formed on thesubstrate. For instance, because the sintering temperature is 850° C. to900° C. in general when the above-mentioned capacitor electrode isformed by way of baking, the capacitor electrode may undergo undesirablediffusion, reaction or the like when the dielectric paste is sintered inthe temperature exceeding 900° C. Therefore, it is desirable to be ableto sinter the dielectric paste at as low a temperature as possible.

SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to provide dielectric paste whichsolves the above-mentioned problem and a thick film capacitor using suchdielectric paste.

The present invention provides a dielectric paste comprising glasspowder, lead perovskite compound dielectric powder and organic vehicle,wherein the glass powder has a composition represented by xBi₂ O₃--yPbO--zSiO₂, where x+y+z is 100 parts (mol) and the values of x, y andz are on lines or within a region enclosed by lines passing through fivepoints A(25, 5, 70), B(10, 20, 70), C(10, 60, 30), D(35, 60, 5) andE(90, 5, 5) on a ternary diagram thereof.

With the above dielectric paste, a minute dielectric film can beobtained even if it is sintered at the relatively low temperature ofless than 870° C., for example. Accordingly, the use of the inventivedielectric paste allows a thick film capacitor which excels in thereliability on the moisture resistance characteristic and the like to beobtained.

In the above dielectric paste, the value of x, y and z is preferably onlines or within a region enclosed by lines passing through four pointsF(15, 30, 55), G(30, 45, 25), H(45, 30, 25) and I(45, 5, 50) on theternary diagram.

With the above preferable dielectric paste, the reliability of thehumidity resistance can be further improved.

In the above dielectric paste, the Curie point of the dielectric powderis preferably within a range from about 120° C. to 500° C.

The above dielectric paste allows a thick film capacitor whosetemperature characteristic of the capacitance shows a positivecharacteristic to be obtained and the thick film capacitor to beadvantageously used specifically as a load capacitor for a ceramicoscillator comprising a resonator having a positive temperaturecharacteristic.

In the above dielectric paste, the glass powder may be within the rangefrom about 35 weight % to about 95 weight % and the dielectric powdermay be contained within the range from about 65 weight % to about 5weight % with respect to the total amount of the glass powder and thedielectric powder. Preferably, the glass is about 40 to 90 wt %. Thedielectric paste allows the dielectric film to be formed as a minutefilm even at such a low temperature value as less than 850° C. forsintering temperature of the dielectric paste.

In the above dielectric paste, the glass powder may comprise more thanabout 80 mol % of main component having the composition represented byxBi₂ O₃ --yPbO--zSiO₂ where x+y+z is 100 parts (mol) and the value of x,y and z are on lines or within a region enclosed by lines passingthrough five points A(25, 5, 70), B(10, 20, 70), C(10, 60, 30), D(35,60, 5) and E(90, 5, 5) on a ternary diagram and less than about 20 mol %of at least one additional component selected from a group comprisingTiO₂, ZrO₂, BaO and SrO. The dielectric constant of the dielectric filmobtained from the dielectric paste containing the glass may be improvedfurther and the control of the capacitance-temperature characteristics(TCC) in the thick film capacitor may be readily made.

The present invention also provides a thick film capacitor comprising adielectric film containing glass and lead perovskite compounddielectric, wherein the glass has a composition represented by xBi₂ O₃--yPbO--zSiO₂ where x+y+z is 100 parts (mol) and the value of x, y and zis on lines or within a region enclosed by lines passing through fivepoints A(25, 5, 70), B(10, 20, 70), C(10, 60, 30), D(35, 60, 5) andE(90, 5, 5) on the ternary diagram.

According to the inventive thick film capacitor, electronic parts suchas a ceramic oscillator can be miniaturized or thinned by incorporatingthis thick film capacitor into the electronic parts instead of adiscrete type capacitor. For instance, the use of the inventive thickfilm capacitor as the load capacitor of a ceramic oscillator allows anoscillator whose oscillating frequency fluctuates less to be obtainedand incorporating this thick film capacitor into the ceramic oscillatorallows the ceramic oscillator to be thinned and miniaturized.

In the above thick film capacitor, the value of the x, y and z ispreferably on lines or within a region enclosed by lines passing throughfour points F(15, 30, 55), G(30, 45, 25), H(45, 30, 25) and I(45, 5, 50)on the ternary diagram.

In the above thick film capacitor, the Curie point of the dielectricsubstance is preferably within a range from about 120° C. to 500° C.

In the above thick film capacitor, the glass may be contained within arange from about 35 weight % to about 95 weight % and the dielectricsubstance may be contained within a range from about 65 weight % toabout 5 weight % with respect to the total amount of the glass powderand the dielectric substance.

In the above thick film capacitor, the glass may comprise more thanabout 80 mol % of main component having the composition represented byxBi₂ O₃ --yPbO--zSiO₂ where x+y+z is 100 parts (mol) and the values ofx, y and z are on lines or within a region enclosed by lines passingthrough five points A(25, 5, 70), B(10, 20, 70), C(10, 60, 30), D(35,60, 5) and E(90, 5, 5) on a ternary diagram and less than about 20 mol %of at least one additional component selected from a group comprisingTiO₂, ZrO₂, BaO and SrO.

The above thick film capacitor may be used as a load capacity elementfor a ceramic oscillator comprising a resonator having a positivetemperature characteristic.

The invention also provides use of the above dielectric paste for athick film capacitor having a dielectric film, wherein the dielectricpaste is used for providing the dielectric film.

The present invention will be better understood from the followingembodiment taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a ternary diagram of xBi₂ O₃ --yPbO--zSiO₂ showing thecomposition range of glass power contained in the inventive dielectricpaste.

FIG. 2 is a section view showing a thick film printed circuit device 2provided with a thick film capacitor 1 fabricated in the first throughthird embodiments of the present invention.

FIG. 3 is section view showing a ceramic oscillator 13 into which thickfilm capacitors 11 and 12 are incorporated and which is fabricated in afourth embodiment of the present invention.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

First Embodiment

FIG. 2 is a section view showing a thick film printed circuit deviceprovided with a thick film capacitor 1 to be fabricated in this firstembodiment. The thick film printed circuit device has a substrate 2 madeof an electrically insulating material and a sub-layer conductor 3, adielectric film 4 and an upper layer conductor 5 facing to the sub-layerconductor 3 via the dielectric film 4. The layers are formedsequentially on the substrate 2.

The dielectric paste of the present invention is used to form theabove-mentioned dielectric film 4. That is, after forming the sub-layerconductor 3 which becomes one of capacitor electrodes of the thick filmcapacitor 1, the dielectric paste is applied on the sub-layer conductor3 and is then sintered to form the dielectric film 4. After that, theupper layer conductor 5 which becomes the other capacitor electrode ofthe thick film capacitor 1 is formed. The characteristics of the thickfilm capacitor 1 thus obtained will be evaluated as described later inthe first embodiment.

The dielectric paste was fabricated as follows. Bi₂ O₃, PbO and SiO₂were prepared as starting materials of a glass component and blended sothat the glass composition (mol %) shown in Table 1 is obtained. Then,the blend thus obtained was melted under a temperature of 1100° C. to1500° C. to make a molten glass. Then, after putting this molten glassinto pure water to quench it, it was crushed to obtain a glass powder.

                  TABLE 1                                                         ______________________________________                                        Sample No. Bi.sub.2 O.sub.3                                                                            PbO    SiO.sub.2                                     ______________________________________                                        1          25            5      70                                            2          10            20     70                                            3          10            60     30                                            4          35            60     5                                             5          90            5      5                                             6          45            5      50                                            7          15            30     55                                            8          30            45     25                                            9          45            30     25                                            10         10            10     80                                            11         0             70     30                                            12         20            70     10                                            13         60            40     0                                             14         70            0      30                                            ______________________________________                                    

The composition of each sample shown in Table 1 is plotted in a ternarydiagram in FIG. 1. In FIG. 1, numbers surround by circles correspond tothe sample Nos. in Table 1.

Meanwhile, a lead perovskite compound ceramic represented by (Pb₀.97Sro₀.03) {(Sb₀.5 Sn₀.5)₀.05 Zr₀.46 Ti₀.49 }O₃ having a Curie point of280° C. was crushed to obtain a dielectric powder.

Next, the glass powder and the dielectric powder were mixed togetherwith an organic vehicle so that the glass powder/dielectricpowder/organic vehicle=35/35/30 (weight %) and were kneaded to preparethe dielectric paste. The organic vehicle here was obtained bydissolving acrylic resin into α-terpineol.

Next, the dielectric paste obtained as described above was used as thedielectric film 4 to fabricate the thick film printed circuit device 1having the thick film capacitor as shown in FIG. 2.

That is, a sub-layer conductor 3, 8 mm in diameter, was formed byproviding an alumina substrate as the substrate 2, by screen-printing aAg/Pd paste thereon and by sintering at 850° C. Next, a 6 mm diameterdisk-shaped dielectric film 4 was formed by screen-printing thedielectric paste prepared in advance on the sub-layer conductor 3 andsintering at a temperature from 850° C. to 890° C. as shown in Table 2.Then, the upper layer conductor 5 having a diameter of 4 mm was formedon the dielectric film 4 by preparing a thermosetting Ag paste, byscreen-printing it on the dielectric film 5 and heating to set it.

Thus, the thick film printed circuit device having the thick filmcapacitor 1 was completed.

Next, in order to determine the characteristics of the thick filmcapacitor 1, i.e. to find the characteristics of capacitance, dielectricloss, dielectric constant and capacity-temperature characteristic (TCC)shown in Table 2, the required measurement was implemented to evaluatethe characteristics of the dielectric film 4. As for the capacitance andthe dielectric loss (tan δ), the measurement was carried out under theconditions of 1 MHz frequency, 1 Vrms voltage and 25° C. temperature andthe dielectric constant (.di-elect cons._(x)) was calculated from theobtained capacitance and the size of the thick film capacitor 1.Further, the insulation resistance (IR) was measured by applying 100 Vof dc voltage for one minute after leaving the samples within anatmosphere of 85° C. temperature and 85% relative humidity. Thecapacity-temperature characteristic (TCC) in temperature from -20° C.through +80° C. was measured under the conditions of 1 MHz frequency and1 Vrms voltage.

                                      TABLE 2                                     __________________________________________________________________________                                 Insulation                                            Sintering    Dielectric                                                                         Dielectric                                                                          Resistance                                       Sample                                                                             Temperature                                                                         Capacitance                                                                          Loss Constant                                                                            log IR                                                                             TCC                                         No.  (° C.)                                                                       (pF)   (%)  ε.sub.x                                                                     (W)  (%/° C.)                             __________________________________________________________________________     1   870   138    1.0  25     >9  0.04                                         2   870   166    1.2  30     >9  0.05                                         3   850   276    1.5  50     >9  0.09                                         4   850   442    1.7  80     >9  0.18                                         5   850   436    1.6  79     >9  0.16                                         6   850   177    1.3  32    >11  0.07                                         7   850   226    1.4  41    >11  0.07                                         8   850   397    1.6  72    >11  0.16                                         9   850   304    1.5  55    >11  0.10                                        10   890   110    0.8  20     >9  0.04                                        11   850   221    1.9  40     <9  0.07                                        12   850   331    2.3  60     <9  0.10                                        13   850   --     --   --    --   --                                          14   850   --     --   --    --   --                                          __________________________________________________________________________

In Tables 1 and 2, Samples 1 through 9 are included within the scope ofthe present invention. As for the composition of the glass powdercontained in the used dielectric paste or of the glass contained in thedielectric film 4 of the obtained thick film capacitor 1, Samples 1through 9 have a composition represented by xBi₂ O₃ --yPbO--zSiO₂ andtheir ratio of composition (x, y, z) falls within a region surrounded byPoint A (25, 5, 70), Point B (10, 20, 70), Point C (10, 60, 30), Point D(35, 60, 5) and Point E (90, 5, 5) in the ternary diagram of FIG. 1.Samples 1 through 9 allow the thick film capacitor 1 to have adielectric constant of 25 through 80, a dielectric loss of less than1.7%, an insulation resistance (IR) which exceeds 9 in terms of log IRafter the humidity test and a temperature coefficient of capacitancehaving a positive inclination of 0.04 to 0.18% to be obtained. Further,Samples 1 through 9 allow the thick film capacitor 1 having theabove-mentioned characteristics to be obtained by the dielectric film 4formed by sintering in a temperature below 870° C.

Note further that for Samples 6 through 9 of the above-mentioned Samples1 through 9, their reliability on humidity testing has been improvedfurther as log IR after the humidity test exceeds 11. As for thecomposition of the glass powder contained in the dielectric paste thusused or of the glass contained in the dielectric film 4 of the thickfilm capacitor 1 thus obtained, Samples 6 through 9 have a compositionrepresented by xBi₂ O₃ --yPbO--zSiO₂ where the ratio of composition (x,y, z) falls within a region surrounded by Point F (15, 30, 55), Point G(30, 45, 25), Point H (45, 30, 25) and Point I (45, 5, 50) on theternary diagram of FIG. 1. It is also noted that the dielectric film 4has been formed by sintering at such a relatively low temperature of850° C in Samples 6 through 9.

In contrast, Sample 10 which is located in the region where there is alarge amount of SiO₂ requires a sintering temperature of 890° C. asshown in Table 2 because the softening point of the glass is too highand the dielectric film 4 can be hardly obtained by sintering in atemperature below 870° C. However, even if it is sintered at thetemperature of 890° C., the thick film capacitor 1 thus obtained has adielectric constant of only 20.

Further, Sample 11 is not preferable because the dielectric loss is aslarge as 1.9% and log IR is less than 9. It is considered that a glasslocated at the region where Sample 11 is positioned is inferior in termsof the minuteness of the dielectric film 4.

Still further, Sample 12 is not preferable because the dielectric lossis as large as 2.3% and log IR is less than 9. It is considered thatglass located at the region where Sample 12 is positioned has a lowvitrification degree and is inferior in terms of the minuteness of thedielectric film 5.

No characteristic values are described in Table 2 as for Samples 13 and14 because they were unmeasurable.

Second Embodiment

The dielectric paste was prepared by mixing the glass powder of Sample 8prepared in the first embodiment and the dielectric powder of the leadperovskite compound used also in the first embodiment so that theirratio is as shown in the following Table 3, and by adding the organicvehicle so that the ratio of the (glass powder+dielectricpowder)/organic vehicle=70/30 (weight %) and kneading. It is noted thatas the organic vehicle, one obtained by dissolving acrylic resin intoα-terpineol was used similarly to the first embodiment.

                  TABLE 3                                                         ______________________________________                                        Sample                  Dielectric                                            No.          Glass Powder                                                                             Powder                                                ______________________________________                                        2-1          95 wt %     5 wt %                                               2-2          90 wt %    10 wt %                                               2-3          70 wt %    30 wt %                                               2-4          50 wt %    50 wt %                                               2-5          40 wt %    60 wt %                                               2-6          35 wt %    65 wt %                                               2-7          30 wt %    70 wt %                                               2-8          10 wt %    90 wt %                                               ______________________________________                                    

Next, the thick film capacitor 1 was fabricated in the same manner withthe first embodiment by using the dielectric paste obtained as describedabove. It is noted that the sintering temperature in forming thedielectric film 5 was set at 850° C. After that, the characteristics ofthe thick film capacitor 1 thus obtained, i.e. the capacitance,dielectric loss, dielectric constant, insulation resistance afterhumidity test and TCC, were found in the same manner with the firstembodiment. Table 4 shows the results.

                  TABLE 4                                                         ______________________________________                                              Capaci-                   Insulation                                    Sample                                                                              tance    Dielectric                                                                             Dielectric                                                                            Resistance                                                                            TCC                                   No.   (pF)     Loss (%) Constant ε.sub.x                                                              log IR (W)                                                                            (%/° C.)                       ______________________________________                                        2-1   138      1.5      25      >9      0.06                                  2-2   160      0.5      29      >9      0.06                                  2-3   304      1.4      55      >9      0.13                                  2-4   397      1.6      72      >9      0.16                                  2-5   447      1.6      81      >9      0.18                                  2-6   491      1.7      89      >9      0.19                                  2-7   530      2.0      96      <9      0.21                                  2-8   784      2.4      142     <9      0.23                                  ______________________________________                                    

As it is apparent from Tables 3 and 4, Samples 2-7 and 2-8 are notpreferable because the dielectric loss exceeds 2.0% and the insulationresistance (IR) after the humidity test is less than 9 in terms of logIR. This shows that the dielectric film 4 cannot be formed as a minutefilm when the sintering temperature of the dielectric paste is 850° C.or less in the present embodiment. It is noted that although thedielectric paste has been printed only once in forming the dielectricfilm 4, it is considered that the insulation after the humidity testwill not increase, though the initial insulation may increase, even ifthe number of times of printing is increased to increase the thicknessof the dielectric film.

In contrast, Samples 2-1 through 2-6 show preferable results in that thedielectric loss is less than 1.7% and the insulation resistance (IR)after the humidity test exceeds 9 in terms of log IR. It can be saidfrom this fact that the ratio of the glass powder and the dielectricpowder contained in the dielectric paste used in forming the dielectricfilm 4 is preferred to be such that glass is within a range from about35 weight % to 95 weight % and the dielectric substance is within arange from about 65 weight % to 5 weight % with respect to the totalamount of the glass and the dielectric substance.

Third Embodiment

The thick film printed circuit device having the thick film capacitor 1shown in FIG. 2 was fabricated.

At first, the dielectric paste for forming the dielectric film 4provided in the thick film printed circuit device was fabricated asfollows. Bi₂ O₃, PbO, SiO₂, TiO₂, ZrO₂ and BaCO₃ were prepared asstarting materials of the glass component and were blended so that theglass composition (mol %) shown in Table 5 is obtained. Then, the blendthus obtained was melted under a temperature of 1100° C. through 1500°C. to make a molten glass in the same manner with the first embodiment.Then, after putting this molten glass into pure water to quench it, itwas crushed to obtain glass powder.

                  TABLE 5                                                         ______________________________________                                        Sample                                                                        No.   Bi.sub.2 O.sub.3                                                                       PbO    SiO.sub.2                                                                            TiO.sub.2                                                                          ZrO.sub.2                                                                           BaO  SrO                              ______________________________________                                        3-1   28       28     24     20                                               3-2   24.5     24.5   21     30                                               3-3   28       28     24          20                                          3-4   24.5     24.5   21          30                                          3-5   28       28     24                20                                    3-6   24.5     24.5   21                30                                    3-7   28       28     24                     20                               3-8   24.5     24.5   21                     30                               3-9   28       28     24     5    5     5    5                                3-10  35       35     30                                                      ______________________________________                                    

In Table 5, the glass powder of Samples 3-1 through 3-9 contain at leastone of TiO₂, ZrO₂, BaO and SrO as an additional component beside themain components of Bi₂ O₃, PbO and SiO₂. Samples 3-1, 3-3, 3-5, 3-7 and3-9 contain 80 mol % main component and 20 mol % additional component.On the other hand, Samples 3-2, 3-4, 3-6 and 3-8 contain 70 mol % maincomponents and 30 mol % additional component. The glass powder of Sample3-10 contains only the main components of Bi₂ O₃, PbO and Sio₂.

Meanwhile, a dielectric powder obtained by crushing the lead perovskitecompound ceramic represented by (Pb₀.97 Sr₀.03) {(Sb₀.5 Sn₀.5)₀.05Zr₀.46 Ti₀.49 }O₃ having Curie point of 280° C. was prepared similarlyto the one used in the first embodiment.

Further, a vehicle obtained by dissolving acrylic resin into α-terpineolwas used as the organic vehicle similarly to that used in the firstembodiment.

Next, the glass powder, dielectric powder and organic vehicle were mixedso that the glass powder/dielectric powder/organic vehicle=35/35/30(weight %) and were kneaded to prepare the dielectric paste.

Next, the dielectric paste obtained as described above was used as thedielectric film 4 to fabricate the thick film printed circuit devicehaving the thick film capacitor 1 as shown in FIG. 2. Here, the thickfilm printed circuit device having the thick film capacitor 1 wascompleted by the same design and method of the first embodiment exceptof that the dielectric paste screen-printed on the sub-layer conductor 3was sintered at a temperature of 850° C. for all the samples in order toform the dielectric film 4 on the sub-layer conductor 3.

After that, the characteristics of the thick film capacitor 1 thusobtained, i.e. the capacitance, dielectric loss, dielectric constant,insulation resistance and capacity-temperature characteristic (TCC),were found in the same manner with the first embodiment. Table 6 showsthe results.

                  TABLE 6                                                         ______________________________________                                              Capaci-                   Insulation                                    Sample                                                                              tance    Dielectric                                                                             Dielectric                                                                            Resistance                                                                            TCC                                   No.   (pF)     Loss (%) Constant ε.sub.x                                                              log IR (W)                                                                            (%/° C.)                       ______________________________________                                        3-1   359      1.8      65      >11     0.09                                  3-2   387      2.4      70      <9      --                                    3-3   353      1.7      64      >11     0.10                                  3-4   419      3.4      76      <9      --                                    3-5   332      1.7      60      >11     0.10                                  3-6   426      2.6      77      <9      --                                    3-7   354      1.8      64      >11     0.16                                  3-8   277      2.9      50      <9      --                                    3-9   381      1.6      69      >11     0.14                                  3-10  293      1.5      53      >11     0.10                                  ______________________________________                                    

TCC measured values for Samples 3-2, 3-4, 3-6 and 3-8 in Table 6 werenot found.

As it is apparent from Tables 5 and 6, Samples 3-1, 3-3, 3-5, 3-7 and3-9 which contain 20 mol % or less of at least one of TiO₂, ZrO₂, BaOand SrO allow the dielectric constant to be improved further as comparedto Samples 3-2, 3-4, 3-6 and 3-8 which contain the same additionalcomponent but more than about 20 mol %.

Further, the control of the TCC or more specifically, the change of theTCC may be relatively readily accomplished by including about 20 mol %or less of the above-mentioned additional component as is apparent bycomparing the Samples 3-1, 3-3, 3-5, 3-7 and 3-9 which contain at leastone of TiO₂, ZrO₂, BaO and SrO at about 20 mol % or less in total and bycomparing Sample 10 which contain no additional component with Samples3-1, 3-3, 3-5, 3-7 and 3-9.

Meanwhile, Samples 3-2, 3-4, 3-6 and 3-8 which contain more than 20 mol% of the additional component have degradation of the dielectric loss(tan δ) and of the insulation resistance. This is considered to havebeen caused because no good dielectric film has been obtained becausethe degree of vitrification of the glass thus obtained might be degradedor the crystal melting temperature might be lowered.

Fourth Embodiment

FIG. 3 is section view showing a ceramic oscillator 13 having thick filmcapacitors 11 and 12 and which is to fabricated in this fourthembodiment.

The ceramic oscillator 13 has a substrate 14 made of an electricallyinsulating material. On the substrate 14, sub-layer conductors 15 and16, dielectric films 17 and 18 and upper layer conductors 19 and 20facing, respectively, the sub-layer conductors 15 and 16 via dielectricfilms 17 and 18 compose the thick film capacitors 11 and 12 are formedsymmetrically and sequentially on the substrate 14.

Conductive adhesives 21 and 22 are applied on the upper layer conductors19 and 20 to electrically connect and to mechanically hold a resonatorelement 23 composed of piezoelectric ceramics to the upper layerconductors 19 and 20 via the conductive adhesives 21 and 22.

The dielectric paste of the present invention is used to form theabove-mentioned dielectric films 17 and 18.

Next, a method for fabricating the ceramic oscillator 13 will beexplained.

At first, 2.5 mm square sub-layer conductors 15 and 16 were formed bypreparing an alumina substrate as the substrate 14, screen printing aAg/Pd paste thereon and sintering at 850° C. Next, 2.0 mm squaredielectric films 17 and 18 were formed on the sub-layer conductors 15and 16 by screen-printing the dielectric paste of Sample 9 in the firstembodiment, Samples 2-4 and 2-5 in the second embodiment and Sample 3-9in the third embodiment on the sub-layer conductors 15 and 16 andsintering them at a temperature of 850° C. Then, 1.5 mm square upperlayer conductors 19 and 20 were formed on the dielectric films 17 and 18by preparing a thermosetting Ag paste, screen-printing it on thedielectric films 17 and 18 and by heating and setting them. Further, theresonator element 23 composed of PZT piezoelectric ceramic was securedon the upper layer conductors 19 and 20 via the conductive adhesives 21and 22. Thus, the ceramic oscillator 13 in which the thick filmcapacitors 11 and 12 are incorporated was completed.

Next, the initial deviation of oscillating frequency, the temperaturecharacteristic of the oscillating frequency (-40° C. to +125° C.) andthe resonance resistance were found for the ceramic oscillator 13 thusobtained. Table 7 shows the results.

                  TABLE 7                                                         ______________________________________                                                Initial       Temperature                                                     Deviation of  Characteristics                                                                          Resonance                                    Sample  Oscillating   of Oscillating                                                                           Resistance                                   No.     Frequency (%) Frequency (%)                                                                            (W)                                          ______________________________________                                        9       0.1           0.03       15                                           2-4     0.08          0.01       15                                           2-5     0.09          0.05       15                                           3-9     0.1           0.02       15                                           ______________________________________                                    

As shown in Table 7, the use of the thick film capacitors 11 and 12composed of the inventive dielectric paste allows a ceramic oscillator13 whose oscillating frequency fluctuates less to be obtained. Further,because the thick film capacitors 11 and 12 may be used as a loadcapacity of the ceramic oscillator 13, the ceramic oscillator 13 may bethinned and miniaturized.

Other Embodiments

Although (Pb₀.97 Sr₀.03) {(Sb₀.5 Sn₀.5)₀.05 Zro₀.46 Ti₀.49 }O₃ has beenused as the lead perovskite compound dielectric substance in theembodiments described above, the present invention is not confined onlyto that. Various lead perovskite compounds of PbTiO₃ system, PbTiO₃--Pb(Mg_(1/3) Nb_(2/3))O₃ system, PbTiO₃ --Pb(Mg_(1/2))O₃ system, PbTiO₃--Pb(Zn_(1/3) Nb_(2/3))O₃ system, PbZrO₃ system, PbZrO₃ --Pb(Mg_(1/3)Nb_(2/3))O₃ system, PbZrO₃ --Pb(Mg_(1/2) W_(1/2))O₃ system, PbZrO₃--Pb(Ni_(1/2) W_(1/2))O₃ system, PbZrO₃ --Pb(Zr_(1/2) Nb_(2/3))O₃system, Pb(Zn_(1/3) Nb_(2/3))O₃ system and the like may be used. Thickfilm capacitors whose temperature coefficient of the capacitance shows apositive characteristic may be obtained by selecting those whose Curiepoint falls within a range from 120° C. through 500° C.

Further, although a vehicle which was obtained by dissolving acrylicresin into α-terpineol has been used as the organic vehicle for thedielectric paste in the embodiments described above, the presentinvention is not confined only to that. In addition, ethyl celluloseresin, nitrocellulose resin, butylal resin and the like may be used asthe resin component and an alcohol type solvent such as butyl carbitol,an ester solvent such as butyl carbitol acetate and acetic ester orkerosene may be used if desired. It is also possible to add aplasticizer such as a phthalate in accordance to the use envisioned.

Further, the inventive dielectric paste may be applied not only inobtaining the thick film capacitor formed on the insulating substratesuch as the alumina substrate as described in the above-mentionedembodiments, but also in forming a capacitor on a dielectric substratesuch as a multi-layered ceramic substrate for example.

Still further, although the sub-layer conductor electrodes 4 or 15 and16 of the thick film capacitor 1 or 11 and 12 was formed of Ag/Pd bymeans of baking and the upper layer conductor 5 or 19 and 20 as theother capacity electrode was formed by the thermosetting Ag paste in theabove-mentioned embodiments, the present invention is not confined onlyto that. Baking type conductors such as Ag, Ag/Pt and Au may be used asthe sub-layer conductor and baking type conductors or thermosettingconductors such as Ag, Ag/Pt, Au, Ag/Pd and Cu may be used as the upperlayer conductor, respectively.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A dielectric paste comprising glass powder, leadperovskite compound dielectric powder and organic vehicle, wherein theglass powder comprises a composition represented by xBi₂ O₃--yPbO--zSiO₂ where x+y+z is 100 mol parts and the values of x, y and zare on lines or within a region enclosed by lines passing through fivepoints A(25, 5, 70), B(10, 20, 70), C(10, 60, 30), D(35, 60, 5) andE(90, 5, 5) on a ternary diagram thereof.
 2. The dielectric pasteaccording to claim 1, wherein the values of the x, y and z are on linesor within a region enclosed by lines passing through four points F(15,30, 55), G(30, 45, 25), H(45, 30, 25) and I(45, 5, 50) on the ternarydiagram.
 3. The dielectric paste according to claim 2 wherein the Curiepoint of the dielectric powder is within a range from about 120° C. to500° C.
 4. The dielectric paste according to claim 3, wherein the glasspowder is about 35 to 95 weight % and the dielectric powder is about 65to 5 weight % with respect to the total amount of the glass powder andthe dielectric powder.
 5. The dielectric paste according to claim 4,wherein the glass powder is more than about 80 mol % of a componenthaving the composition represented by xBi₂ O₃ --yPbO--zSiO₂ and lessthan about 20 mol % of at least one additional component selected fromthe group consisting of TiO₂, ZrO₂, BaO and SrO.
 6. The dielectric pasteaccording to claim 1 wherein the Curie point of the dielectric powder iswithin a range from about 120° C. to 500° C.
 7. The dielectric pasteaccording to claim 6, wherein the glass powder is about 35 to 95 weight% and the dielectric powder is about 65 to 5 weight % with respect tothe total amount of the glass powder and the dielectric powder.
 8. Thedielectric paste according to claim 7, wherein the glass powder is morethan about 80 mol % of a component having the composition represented byxBi₂ O₃ --yPbO--zSiO₂ and less than about 20 mol % of at least oneadditional component selected from the group consisting of TiO₂, ZrO₂,BaO and SrO.
 9. The dielectric paste according to claim 1, wherein theglass powder is about 35 to 95 weight % and the dielectric powder isabout 65 to 5 weight % with respect to the total amount of the glasspowder and the dielectric powder.
 10. The dielectric paste according toclaim 1, wherein the glass powder is more than about 80 mol % of acomponent having the composition represented by xBi₂ O₃ --yPbO--zSiO₂and less than about 20 mol % of at least one additional componentselected from the group consisting of TiO₂, ZrO₂, BaO and SrO.
 11. Athick film capacitor comprising a dielectric film containing glass andlead perovskite compound dielectric substance, wherein the glasscomprises a composition represented by xBi₂ O₃ --yPbO--zSiO₂ where x+y+zis 100 mol parts and the values of x, y and z are on lines or within aregion enclosed by lines passing through five points A(25, 5, 70), B(10,20, 70), C(10, 60, 30), D(35, 60, 5) and E(90, 5, 5) on a ternarydiagram thereof.
 12. The thick film capacitor according to claim 11,wherein the value of the x, y and z are on lines or within a regionenclosed by lines passing through four points F(15, 30, 55), G(30, 45,25), H(45, 30, 25) and I(45, 5, 50) on the ternary diagram.
 13. Thethick film capacitor according to claim 12, wherein the Curie point ofthe dielectric substance is within a range from about 120° C. to 500° C.14. The thick film capacitor according to claim 13, wherein the glass isfrom about 35 to 95 weight % and the dielectric substance is from about65 to 5 weight % with respect to the total amount of the glass powderand the dielectric substance.
 15. The thick film capacitor according toclaim 14, wherein the glass comprises more than about 80 mol % of maincomponent having the composition represented by xBi₂ O₃ --yPbO--zSiO₂and less than about 20 mol % of at least one additional componentselected from the group consisting of TiO₂, ZrO₂, BaO and SrO.
 16. Thethick film capacitor according to claim 11, wherein the Curie point ofthe dielectric substance is within a range from about 120° C. to 500° C.17. The thick film capacitor according to claim 11, wherein the glass isfrom about 35 to 95 weight % and the dielectric substance is from about65 to 5 weight % with respect to the total amount of the glass powderand the dielectric substance.
 18. The thick film capacitor according toclaim 11, wherein the glass comprises more than about 80 mol % of maincomponent having the composition represented by xBi₂ O₃ --yPbO--zSiO₂and less than about 20 mol % of at least one additional componentselected from the group consisting of TiO₂, ZrO₂, BaO and SrO.
 19. Aceramic oscillator comprising a resonator having a positive temperaturecharacteristic and the thick film capacitor according to claim
 13. 20. Aceramic oscillator comprising a resonator having a positive temperaturecharacteristic and the thick film capacitor according to claim 16.